compat: define tfind family of functions regardless of the search.h status

The existence of search.h is not relevant for that. search.h may exist but does
not provide tfind, as on Windows.

If tfind.c is included for compilation, then the code needs to be built.

compat/tfind.c

@@ -6,9 +6,6 @@
 # include <config.h>
 #endif
 
-/** search.h is not present so every t* functions has to be implemented */
-#ifndef HAVE_SEARCH_H
-
 #include <assert.h>
 #include <stdlib.h>
 
@@ -240,5 +237,3 @@ twalk(const void *vroot, cmp_fn_t action) /* Root of the tree to be walked */
 	if (vroot != NULL && action != NULL)
 		trecurse(vroot, action, 0);
 }
-
-#endif // HAVE_SEARCH_H

include/vlc_fixups.h

@@ -481,7 +481,7 @@ ssize_t sendmsg(int, const struct msghdr *, int);
 #endif
 
 /* search.h */
-#ifndef HAVE_SEARCH_H
+#ifndef HAVE_TFIND
 typedef enum {
     preorder,
     postorder,
@@ -498,7 +498,7 @@ void twalk( const void *root, void(*action)(const void *nodep, VISIT which, int
 void *lfind( const void *key, const void *base, size_t *nmemb,
              size_t size, int(*cmp)(const void *, const void *) );
 #endif
-#endif /* HAVE_SEARCH_H */
+#endif /* HAVE_TFIND */
 
 #ifndef HAVE_TDESTROY
 void tdestroy( void *root, void (*free_node)(void *nodep) );